This invention relates generally to ordnance proximity fuzes and, more particularly, to a high altitude doppler ordnance fuze.
Non-contacting ordnance fuzes utilizing the doppler effect, that is, the frequency shift due to the relative motion between the fuze and the desired target, are well known in the ordnance art. These ordnance fuzes transmit either a continuous signal or a pulse signal toward a target and, consequently, may be classified according to their mode of operation as continuous (CW) doppler or pulse doppler fuzes, respectively. If the CW doppler fuze is utilized in an aerial ordnance device, such as a bomb or the like, approaching a relatively stationary target, such as ground level, the doppler signature of the approaching target is a sinusoidal waveshape with a hyperbolic varying amplitude, that is, an amplitude having an instantaneous value inversely proportional to the height above ground level.
While CW doppler fuzes have operated satisfactorily at relatively low altitudes above ground, accurate functioning at higher altitudes above ground is exceedingly difficult because of the small incremental variation in the hyperbolic amplitude of the doppler signature at these higher altitudes.
Pulse doppler fuzes have provided operation at somewhat higher altitudes than CW doppler fuzes. Pulse doppler ordnance fuzes detect targets during the transmitted pulse only and, therefore, the hyperbolic doppler signature provided by CW fuzes is modified in that a doppler signal is detected only during interaction between the transmitted pulse and received echo pulse. The altitude at which interaction between the transmitted and received echo pulses first occurs is termed the range cutoff. As the pulse doppler fuze approaches a target, the doppler signature amplitude will suddenly increase from a zero value at altitudes above range cutoff to a non-zero value below range cutoff and then follow a hyperbolic pattern similar to that of CW doppler fuzes. This sudden change in doppler signature at range cutoff may be utilized advantageously to detonate the ordnance device at the range cutoff altitude which is somewhat higher than altitudes obtainable with CW doppler fuzes.
Generally, the designer of a pulse doppler ordnance fuze has little or no control over the range cutoff, which is a function of pulse width of the transmitted signal and is determined by other design requirements such as, for example, oscillator size, power requirements, etc. Thus, heretofore employed conventional pulse doppler fuzes are limited in operation to altitudes at or below range cutoff and, therefore, have been unable to provide high altitude operation. Furthermore, prior art pulse doppler fuzes are sensitive to countermeasure techniques, or the like, especially in the duration between pulses during which time oscillators utilized therein are in the regenerative region.
Application Ser. No. 14,833 filed by John J. Nastronero on Feb. 16, 1970, and of common assignee herewith, discloses a pulse doppler ordnance fuze which utilizes a radio frequency oscillator and modulator therefor which drives the oscillator from a CW mode to a pulse mode of operation thereby achieving improved countermeasure protection by not allowing the oscillator to enter the regenerative region between pulses. However, the pulse doppler fuze disclosed therein is not operable at altitudes above range cutoff.